The Northstar Cam Bearing Caps: A New Application for Aluminum P/M

A new application for the use of aluminum powder metallurgy in automotive engines has been developed. The dual overhead cam Northstar engine which began production in the 1993 model year uses aluminum metal powder for the camshaft bearing caps in the cylinder head assembly. The material was chosen because it offered the opportunity to eliminate both the machining operations and the capital required for the machines when compared to traditional die cast bearing caps. Tolerances for the P/M cap were essentially the same as those for traditional machining operations, and from a functional perspective, they performed equally as well as the die cast parts.

Cam bearing caps for overhead cam engines are typically made as high pressure aluminum die castings which are subsequently machined to provide flat mating surfaces, bolt holes, and many other features. After assembly to the cylinder head, the caps are generally line bored to provide an accurate and straight series of holes for the camshaft. In the early design stages of the Northstar engine a new approach to the manufacture of the bearing caps was investigated as an opportunity to reduce the number of machining processes and the capital required for such high production manufacturing processes. The use of aluminum powder metal, which can be used with no machining operations except for line boring was developed. This paper will detail some of the basics of aluminum powder metallurgy and the application for the Northstar engine.